1. Field of Invention
The present invention relates to a method of inspecting the discharge state of a nozzle, and a discharge state inspection mechanism, that decide whether or not fluid droplets are discharged normally from the nozzle based on the electrical change that is produced when a potential difference is produced between a fluid discharge head and an opposing head cap, fluid droplets are discharged from a nozzle of the fluid droplet discharge head, and the fluid droplets charged by the potential difference land on the head cap. The invention also relates to a fluid droplet discharge device in which this discharge state inspection mechanism is disposed.
2. Description of Related Art
When the nozzles of the inkjet head become clogged, air bubbles are left inside a nozzle, or foreign matter clings to the nozzle surface in a fluid droplet discharge device such as an inkjet printer, the ink droplets will not be discharged normally from the nozzle. If the ink droplets are not discharged normally, printing defects such as part of the desired printout not being printed or the desired color not being printed because a specific color of ink is not discharged can occur. As a result, when inkjet printers are used in medical facilities, for example, to print labels that are applied to drugs and other medical products, the ink discharge state of the nozzles is inspected to confirm that the ink discharge state is normal before starting to print, thereby helping to prevent treatment errors that can result from color printing errors and problems reading labels as a result of such printing defects.
An inkjet printer having an ink discharge state inspection mechanism for inspecting the ink discharge state of the nozzles is taught in Japanese Unexamined Patent Appl. Pub. JP-A-2003-118133, for example.
As an ink discharge state inspection mechanism JP-A-2003-118133 teaches forming a potential difference between an inkjet head and an opposing head cap, discharging ink droplets from the nozzles of the inkjet head, detecting the voltage change produced by the induced current that occurs temporarily when the ink droplets charged by the potential difference land on the head cap, and determining that the ink droplets are discharged normally from the nozzle if the maximum amplitude of this voltage change is greater than or equal to a threshold value.
Because a specific induced current is produced if the ink discharge state is normal, this ink discharge state inspection mechanism can get a waveform that attenuates gradually from the initial amplitude by detecting this voltage change. A waveform with the specific amplitude cannot be acquired if the ink droplets are not discharged normally because the specific induced current is not produced. The ink discharge state of the nozzle can therefore be determined normal if the maximum amplitude of the voltage change is greater than or equal to the threshold value.
The circuit board for determining if the ink discharge state is normal or not must be located at a position separated from the head cap so that the droplets do not land on the circuit board. This means that the induced current produced inside the head cap must be input to the circuit board through a wire lead, for example. As a result, if when the circuit board is inspecting the ink discharge state the operator touches the inkjet printer such that vibration or shock is temporarily externally applied to the ink discharge state inspection mechanism, causing the wire lead to quiver, this vibration of the wire lead can disrupt the induced current that is produced, possibly resulting in false detection of a voltage change exceeding the threshold value. In other words, if a momentary external shock is applied, the ink discharge state of the nozzles can be determined to be normal even though the ink droplets are not being discharged normally from the nozzles.